1. Field of the Invention
This invention relates to a toner used in recording processes carried out by electrophotography, electrostatic recording, magnetic recording and toner-jet recording, a process for producing the toner, and an image-forming method employing the toner. More particularly, the present invention relates to a toner used in image-recording apparatus utilizable in copying machines, printers, fax machines, plotters and so forth, a process for producing the toner, and an image-forming method employing the toner.
2. Related Background Art
Various methods are conventionally proposed as electrophotography in U.S. Pat. No. 2,297,691, Japanese Patent Publications No. 42-23910 and No. 43-24748 and so forth. Methods by which electrostatic latent images are developed include dry-process development and wet-process development. Also, the dry-process development is grouped into a method employing a two-component developer and a method employing a one-component developer. Toners used in the dry-process development are commonly colored fine resin particles containing a binder resin, a colorant and a wax as chief constituents. Usually, they have a particle diameter of about 6 xcexcm to about 15 xcexcm as number-average particle diameter. As processes for producing toners comprised of such colored fine resin particles, commonly used is a production process, what is called pulverization, in which a binder resin, a colorant such as a dye or pigment and/or a magnetic material, a wax and so forth are melt-kneaded, the kneaded product obtained is cooled and thereafter pulverized and the pulverized product obtained is further classified to obtain a toner.
Toners produced by such a process must be so made up as to have positive or negative electric charges in accordance with the charge polarity of electrostatic latent images to be developed. To make a toner have electric charges, the triboelectric chargeability of a binder resin, which is a chief constituent of the toner, may be utilized, but such a means alone can not impart a sufficient charging performance to a toner. Accordingly, in order to impart the desired triboelectric chargeability to toners, a charge control agent is added. Toners containing such a charge control agent can provide a relatively large quantity of triboelectricity, but may commonly cause a lowering of the quantity of triboelectricity in an environment of high humidity and on the other hand a lowering of toner""s charging rate in an environment of low humidity.
One of the causes thereof is considered to be the adsorption of moisture that occurs in the vicinity of the charge control agent contained in toner particles and at toner particle surfaces. More specifically, it is considered that in the environment of high humidity the moisture is adsorbed to the charge control agent in a large quantity to lower the quantity of triboelectricity and that in the environment of low humidity the moisture is adsorbed to the charge control agent in a small quantity and hence the resistance becomes higher to lower the charging rate.
Nowadays, as charge control agents known in the present technical field, negatively chargeable ones include metal salts of monoazo dyes and copper phthalocyanine pigments.
Most of the charge control agents, though having a sufficiently high charge-providing ability, have so poor a charge controllability that there has been limitations on binder resins and other materials which are usable in combination.
Japanese Patent Applications Laid-open No. 63-33755, No. 2-190869, No. 2-230163 and No. 4-347863 disclose toners making use of salicylic acid or derivatives thereof as charge control agents. The salicylic acid, however, not only makes charge controllability greatly variable depending on temperature and humidity but also has sublimation properties, and hence toner""s storage conditions are greatly restricted. Also, salicylic acid derivatives have a good dispersibility to binder resins, and hence toner""s matching to image-forming apparatus can be improved to a certain extent. However, it has been necessary to add them in a large quantity in order for them to exhibit the desired charge controllability.
Japanese Patent Applications Laid-open No. 61-238846 and No. 5-134457 disclose toners obtained by depositing a charge control agent on toner particle surfaces in order to attain a uniform charge-providing ability. Such a method certainly makes toner""s charging performance stable. However, as a result of running on many sheets, the charge control agent may come off the toner particle surfaces to become less effective to cause a problem on the running performance of toners.
Japanese Patent Application Laid-open No. 3-84558 also discloses a toner prepared by first producing spherical particles, thereafter immersing the spherical particles in an organic solvent in which a charge control agent pigment has been dissolved or dispersed, and then controlling the concentration of the charge control agent pigment on the particle surface to a stated range while washing off any unwanted matter. However, the charge control agent pigment on particle surfaces of the toner obtained by such a method stands dispersed non-uniformly, and causes a problem on toner""s matching to image-forming apparatus. Also, since the pigment is used, it is difficult to use the toner as a color toner.
In recent years, as electrophotographic images are sought to have much higher image quality and much higher resolution, toners are required to have smaller particle diameter and higher function. Under such circumstances, processes for producing toners by polymerization have attracted notice. For example, as the processes for producing toners by polymerization, Japanese Patent Publications No. 36-10231 and No. 51-14895 and Japanese Patent Application Laid-open No. 53-17735 disclose processes for producing toners by suspension polymerization. In the processes, a colorant and further optionally a polymerization initiator, a dispersant, a cross-linking agent, a charge control agent, a release agent, a polar resin and other additives are dissolved or dispersed in a polymerizable monomer which is a material for a binder resin, thus a polymerizable monomer composition is prepared. The polymerizable monomer composition thus obtained is introduced into an aqueous dispersion medium containing a dispersion stabilizer, having been prepared beforehand, to carry out granulation by the use of a stirrer to form particles of fine particle size, and thereafter polymerizable monomers present in the granulation particles are polymerized to solidify the particles, followed by filtration, washing and then drying to obtain toner particles having the desired particle diameter and composition.
Such toners produced by polymerization are toners having a small particle diameter which enable formation of images having a good quality, and have a sharp particle size distribution. Hence, they have superior matching to image-forming apparatus.
However, in the suspension polymerization in which polymerizable monomers present in granulation particles formed in an aqueous dispersion medium are polymerized, the granulation particles and the aqueous dispersion medium come into contact in so large a contact area that any toner constituent material having many polar groups tends to dissolve out of the interior of granulation particles into the aqueous dispersion medium, so that the toner constituent material having many polar groups that is present at toner particle surfaces and in the vicinity of the surfaces may become non-uniform in its content. Thus, it has been difficult to obtain toners having charging performance with a superior environmental stability.
Studies made by the present inventors have revealed that, when a toner containing an oxycarboxylic acid such as salicylic acid is produced by such suspension polymerization, the oxycarboxylic acid may so seriously dissolve into the aqueous dispersion medium that the oxycarboxylic acid present at toner particle surfaces and in the vicinity of the surfaces may become non-uniform in its content to cause problems such that the charging performance is affected by temperature and humidity to vary greatly and, due to poor matching to image-forming apparatus, a toner-carrying member is contaminated with toner.
An object of the present invention is to provide a toner having solved such problems the prior art has had, and a process for producing the toner.
More specifically, an object of the present invention is to provide a toner which has superior environmental stability and charging performance and enables high-quality images to be formed stably over a long period of time, and a process for producing such a toner.
Another object of the present invention is to provide a toner which is highly applicable to electrophotographic processes and free of adverse effect on a toner-carrying member, etc. such as contamination, and a process for producing such a toner.
Still another object of the present invention is to provide an image-forming method suited to development according to a one-component contact development system.
A further object of the present invention is to provide an image-forming method suited to a cleaning-at-development system in which the toner remaining on the surface of an image-bearing member after the step of transfer is collected by a developing assembly simultaneously in the step of development.
A still further object of the present invention is to provide an image-forming method that enables formation of stable images over a long period of time without causing any faulty images due to faulty charging, even in a contact charging system making use of a contact charging member.
A still further object of the present invention is to provide an image-forming method that enables formation of stable images over a long period of time while reducing transfer residual toner and without causing any faulty images due to faulty charging, even in a contact transfer system making use of a contact transfer member.
A still further object of the present invention is to provide an image-forming method promising a superior running performance, that can smoothly collect transfer residual toner at the time of development even when applied in a higher-speed image-forming process, and enables formation of stable images over a long period of time by virtue of stable developing performance.
To achieve the above objects, the present invention provides a toner comprising toner particles containing at least a binder resin, a colorant, a wax component and an oxycarboxylic acid, wherein:
where the weight of oxycarboxylic acid extracted with methanol from 1 g of the toner is represented by A (mg) and the weight of oxycarboxylic acid extracted with 0.1 mol/liter of an aqueous sodium hydroxide solution from 1 g of the toner is represented by B (mg), the toner satisfies:
1.05xe2x89xa6A/Bxe2x89xa63.00,
and
0.10xe2x89xa6Bxe2x89xa63.50.
The present invention also provides a process for producing a toner, comprising:
a granulation step of dispersing in an aqueous dispersion medium a polymerizable monomer composition containing at least a polymerizable vinyl monomer, a colorant, a wax component, a polymerization initiator and an oxycarboxylic acid, to form particles of the polymerizable vinyl monomer composition; and
a polymerization step of polymerizing the polymerizable vinyl monomer present in the particles of the polymerizable monomer composition to form toner particles;
wherein the reaction to polymerize the polymerizable vinyl monomer in the course of from the granulation step to the polymerization step comprises a first reaction step carried out to enhance the polymerization conversion of the polymerizable vinyl monomer to 10% or higher while keeping pH of the aqueous dispersion medium at 4.5 to 8.5, and a second reaction step carried out after the first reaction step while adjusting pH of the aqueous dispersion medium to 9 to 13 to further enhance the polymerization conversion.
The present invention still also provides a process for producing a toner, comprising:
a granulation step of dispersing in an aqueous dispersion medium a polymerizable monomer composition containing at least a polymerizable vinyl monomer, a colorant, a wax component, a polymerization initiator and an oxycarboxylic acid, to form particles of the polymerizable monomer composition;
a polymerization step of polymerizing the polymerizable vinyl monomer present in the particles of the polymerizable monomer composition to form toner particles;
a distillation step of removing the polymerizable vinyl monomer remaining in the toner particles;
a filtration step of solid-liquid separating the toner particles from the aqueous dispersion medium; and
a washing step of washing the toner particles;
wherein the reaction to polymerize the polymerizable vinyl monomer in the course of from the granulation step to the polymerization step is carried out in the aqueous dispersion medium at pH of 4.5 to 8.5, and then, after pH of the aqueous dispersion medium is adjusted to 9 to 13, the distillation step is carried out at a temperature not lower than the glass transition temperature of the binder resin of the toner.
The present invention further provides an image-forming method comprising:
a charging step of charging an image-bearing member for holding thereon an electrostatic latent image;
an exposure step of subjecting the image-bearing member thus charged, to exposure to form an electrostatic latent image;
a developing step of developing the electrostatic latent image by the use of a toner held on the surface of a toner-carrying member, to from a toner image; and
a transfer step of transferring the toner image formed on the image-bearing member, to a transfer medium via, or not via, an intermediate transfer member;
wherein;
the toner comprises toner particles containing at least a binder resin, a colorant, a wax component and an oxycarboxylic acid; and
where the weight of oxycarboxylic acid extracted with methanol from 1 g of the toner is represented by A (mg) and the weight of oxycarboxylic acid extracted with 0.1 mol/liter of an aqueous sodium hydroxide solution from 1 g of the toner is represented by B (mg), the toner satisfies:
1.05xe2x89xa6A/Bxe2x89xa63.00,
and
0.10xe2x89xa6Bxe2x89xa63.50.